A turbo compound is a system for increasing an axle driving force. A known turbo compound rotates a turbine with exhaust gas of an engine to transmit the output of the turbine to a crank shaft via a gear or a coupling, or rotates a generator with exhaust gas to extract and utilize electric energy.
For instance, Patent Document 1 (JP2008-175126A) discloses an electric turbo compound which, in a schematic configuration based on FIG. 9, includes an energy recovery part 010 which recovers energy by sucking in a part or all of exhaust gas discharged from a turbine 01a of a turbocharger 01 including the turbine 01a and a compressor 01b, a valve 07 capable of changing the ratio of exhaust gas to be sucked into the energy recovery part 010, and a valve controller 08 for controlling the valve 07 to be open or closed in accordance with a predetermined control pattern.
Further, Patent Document 2 (JP2010-190145A) discloses a configuration including an electric compressor 3 driven by an electric motor 3m to rotate to compress air, thereby supplying the compressed air to an internal combustion engine 7, a turbine generator 2 for generating power by driving a generator 2g with a turbine 2t driven by exhaust gas from the internal combustion engine 7, and a storage unit 12 for storing electric power generated by the turbine generator 2 and supplying the electric power to the electric compressor 3 (see FIG. 2).
Further, Patent Document 3 (JPH6-323158A) discloses recovering energy by driving a turbocharger with exhaust energy of exhaust gas supplied to the turbocharger through the first exhaust port in the first half of an exhaust process, in which combustion gas has a sufficient flow rate, and increasing an engine output by recovering energy of exhaust gas corresponding to a decrease in a back pressure at a turbine inlet of an energy recovery device to which exhaust gas is supplied through the second port bypassing the turbocharger in the second half of the exhaust process, in which the flow rate of the combustion gas is low.